Organophosphates and carbamates once dominated nematode control strategies. It is worth pausing here to recollect why Nemacur (Fenamiphos) was so effective and widely used, especially in North America:
(1) It had systemic activity.
(2) The neurotransmission pathway it targeted (relying on acetylcholinesterase activity) is common across all nematode species. This meant that to control a particular nematode pest, the application timing was less important, all stages of nematode development could be targeted and it didn’t really matter which type of nematode was causing the trouble.
Today the nematicide market is completely different having moved towards less dangerous chemistries (e.g. Fluopyram, Abamectin and Fluensulfone). While recent research suggests Naphthoquinones & Spirotetramat might be future control options in turf, and new chemistries may continue to emerge, the number of registered nematicide products on offer has generally diminished globally. In Europe many countries are leaning towards implementing pesticide-free policies entirely and this has led us to change the way we think about nematode problems as a whole.
Currently across the British Isles there is just one active product registration that specifies nematode control in turf (Eagle Green Care (EGC) which is a garlic extract, which comes as a liquid or granular formulation. Before we look at how this product works as an example of a non-systemic chemistry, let us consider how endoparasitic nematodes live their lives.
The ‘root knot’ (Meloidogyne spp), ‘cyst’ (Heterodera spp), and ‘root gall’ (Subanguina spp) nematodes top the shortlist of root dwelling endoparasites that might warrant management consideration (Figure 1). While there are major differences between these nematodes, they all share the following core elements of the life cycle. Starting from an egg, a second stage juvenile emerges. It leaves the safety of the old infection site and enters the rootzone, seeking out a new root tip to infect.
Figure 1: Timeline of a typical root knot nematode life cycle – in cool season turf maturity is similar, however it can take up to 12 weeks to complete and eggs are often laid inside the roots.
N = nematode GC = giant cell Xy = xylem Ph = phloem En = endodermis
Once the nematode finds its target, it bypasses the epidermis and cortex to reach vascular tissues. Here it selects cells to reprogramme to its advantage. These cells become enlarged, resulting in characteristic root deformities and it is here the nematode feeds until maturity. Egg deposition then follows, completing the cycle. Endoparasites therefore only leave plant tissues for relatively short periods of time and this it is here where these types of nematodes are most vulnerable to treatment.
Newer nematicides have limited (if any) systemic activity. However, their impact is just as effective, as Nemacur (Fenamiphos) was provided, that they make direct contact with the nematodes causing the problem. This is the key concept for utilising a non-systemic acting nematicide (applications should be timed with peak hatching). This is why effective management of endoparasitic nematodes integrates knowledge of site-specific challenges, nematode life cycles and seasonal behaviour. EGC is formulated to contain a unique fingerprint of compounds found in garlic including diallyl polysulfides. These react with low molecular weight thiols, altering the ability of an organism to buffer against redox imbalances created during natural processes like respiration.
Nematodes exposed to EGC begin to show mobility reduction in approximately 2 hours and death can occur in as little as 24 hours. In other words, it is fast acting and timing is critical for successfully reducing populations (Figure 2).
Figure 2: The impact of polysulfide concentration (DAS) and duration of exposure on the model worm Steinernema feltiae.
Because nematodes do not typically move very far horizontally by themselves (realistically less than 30cm per year), an initial population can multiply in a segregated manner and symptoms can return annually in the same locations. Many symptoms of plant parasitic nematode infection are due to elevated stress in the plants, at levels above which they can cope. Symptoms often correlate with either the timing of female development (because of energy demand from the pest) or post-hatching (because of physical damage and root degradation).
Subanguina spp infect Poa spp and while peak hatching activity is expected in the summer, they can complete their life cycle continually, while environmental conditions allow. Heterodera spp typically hatch once per year (when soils are cooler from November onwards), developing into females over spring and summer, and can infect all turf types. Meloidogyne spp are the most challenging to control, typically hatching up to three times per year and also infect all turf types. Because hatching patterns do not usually overlap, controlling multiple types of nematodes can be extremely challenging.
Following the hatch of an endoparasite, a lot of physical damage occurs. Root tissue can be lost below the point of infection, resulting in a more shallow root system with each sequential hatch. This is one aspect of plant health decline that biostimulant products can help with.
Some products can help replace the tissues that will ultimately be lost, and establish root depths where water is available, in time for the periods of the year when abiotic stress peaks. Biostimulant products can also alter microbial profiles of bacteria and fungi in the rootzone, so starting a programme early is therefore important. In addition to cultural practices to reduce stress, using biostimulants and plant derived secondary metabolites to ‘help the plants to help themselves’, would seem to be the way the industry is taking on this challenge!
References & Further Reading:
Meloidogyne Life Cycle: http://www.rootbiologynews.com/2013/12/root-knot-nematodes-induce-plants-to.html
Cyst Life Cycle:
https://doi.org/10.1111/j.1364-3703.2005.00306.x
Subanguina Radicicola Information:
https://apsjournals.apsnet.org/doi/10.1094/PDIS.2003.87.10.1263C
EGC background information and Nematicidal Activity of DAS:
https://ueaeprints.uea.ac.uk/id/eprint/50025/1/PhDMiriamArbach2014.pdf
Biostimulant Influences on Agrostis stolonifera:
https://journals.ashs.org/downloadpdf/journals/hortsci/40/6/article-p1904.pdf
Microbial Communities in Managed Amenity Turf:
https://www.sciencedirect.com/science/article/abs/pii/S0038071707000284
https://apsjournals.apsnet.org/doi/full/10.1094/PBIOMES-03-21-0021-R
About the Author
Dr. Deborah Cox
Technical Advisor To Turfgrass®
Dr. Deborah Cox began her career in molecular biology 18 years ago in Dundee, Scotland graduating in forensic science. She then completed a PhD at Queens University Belfast, Northern Ireland in 2015 where she studied the genetics behind osmotic stress response in plants.
She then developed advanced molecular biology skills during her post-doctoral project at the John Innes Centre in Norwich, England, before returning to Belfast to work on molecular interactions between plants and plant parasitic nematodes (firstly at Queens University Belfast, and then at the Agri Food and Biosciences Institute). She was the Pest and Pathogen Diagnostics Lab Manager during her time at the Agri Food and Biosciences Institute, which used molecular biology techniques to confirm quarantine organisms and support early detection of pests that require management plans. She is now the Principal Investigator and Managing Director in Lagan Valley Scientific’s Turf Clinic, which aims to support the amenity industry in managing turf pests and diseases.